One of the universal elements found in the design and manufacture of products is the gasket or seal. Many industries, such as those in automotive, appliance, and packaging activities, use large amounts of gaskets for water sealing, dust sealing, air sealing, and the like. In many cases, the gaskets are in the form of custom-designed molded pieces or are supplied in roll form. In the latter situation, the user cuts a length from the roll and places it manually in the desired location in his product. In both cases (molded piece and roll form), there is a manual operation that is not only expensive, but does not fit into an automatic assembly line. In present-day manufacturing, in order to attain efficiency and to maintain a competitive position, it is necessary to have automation and low labor costs.
In order to overcome the above objections, the concept of forming a gasket "in place" has been developed i.e., making the gasket on the surface of the product with which it is to be used. This procedure is very promising and constitutes a growing sector in those industries that use gaskets. As a matter of fact, the installation of gasket forming "in place" has been proposed by several companies, particularly those manufacturing and selling robotic systems.
In general, the automatic forming of a gasket on the surface of a product requires the use of several techniques, namely robotics, material handling, and material compounding. Such an installation would typically consist of an automatic gun fed by a metering pump system operating through a mixing device for evenly mixing a two-component material, such as used for generating polyurethane. The gun is driven by a robot arm along an appropriate path while extruding the required amount of material. In such installations, the heaviest investment is in the robot, which is usually a 2 or 3 axis portic type. The handling equipment usually consists of two metering pumps, each handling one of the two reactive components of the material to be used for the gasket. These metering pumps supply appropriate amounts of each component and introduce them to a static or dynamic mixing device.
In the past, the material used has generally been a two-part flexible polyurethane, which can be foamed or unfoamed. If the material is foamed, this is usually accomplished by the use of CO.sub.2 generated by the reaction of one of the components with moisture contained in the other component. Low viscosity components are usually used, since it is easier to mix them.
The low viscosity components of such a system are very appropriate in the case of a flat gasket, i.e., a gasket applied to a single plane surface and where the cross-sectional shape can be a substantially semi-oval shape. Because of their low viscosity, such materials will not hold other shapes (rectangular or triangular, for instance) and, because they are liquid, a tridimensional (x, y, z) application is not possible; in such a case, the material will flow and will not hold a uniform shape.
While certain high-viscosity materials do not have this deficiency, they have other problems. For instance, if a bead of high viscosity material is laid by extrusion onto a surface in the shape of a closed figure, the cross-sectional shape may be indeterminate at the point where the "ends" of the extrusion come together. The ends will either be somewhat separated and leave a section of reduced cross-sectional area or they will overlap and produce a section of greater than desired cross-sectional area. Either of these situations is unacceptable where a gasket of absolutely uniform shape and cross-sectional area is desired.
It can be seen, then, that a low viscosity gasket material is limited to single plane surfaces where the cross-sectional shape is unimportant, while high-viscosity materials give problems at the "start and stop" location. These and other difficulties experienced with the prior art systems have been obviated in a novel manner by the present invention.
It is therefore, an outstanding object of the invention to provide a method for forming a gasket in place on a surface that lies in other than a single plane.
Another object of the invention is the provision of a process for the "in place" application of a gasket material with a desired cross-sectional shape that is other than a natural liquid bead.
A further object of the present invention is the provision of a method for forming a gasket of highly viscous material in a closed figure and with a uniform cross-sectional shape even at the "start and stop" position.
It is another object of the present invention to provide a method for forming an annular gasket "in place" with a uniform cross-sectional shape though the entire length.
A still further object of the invention is the provision of gasket which is formed in place and which has a uniform cross-sectional form and area throughout.
It is a further object of the invention to provide apparatus for forming an annular gasket in place with a uniform cross-sectional shape in its entire length.
With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.